At least four people have been detained in Moscow outside the building of Russia's Investigative Committee, after activists started what they call an "Occupy the Investigative Committee" campaign.

About 100 people were taking part in the action to demand the release of those still detained in connection with an antigovernment rally in Moscow on May 6.

Police detained the four activists shortly after people started gathering outside the committee's building.

Among those still reported outside the building was Sergei Udaltsov, leader of the opposition Left Front, who said the "picket" was a "sign of protest against the repressive actions toward the opposition activists."

On June 12, tens of thousands attended a sanctioned antigovernment rally in Moscow.